MODIS comparisons with northeastern Pacific in situ stratocumulus microphysics

Noble, Stephen; Hudson, James G.

doi:10.1002/2014jd022785

Cited by 27 publications

(43 citation statements)

References 34 publications

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“…The marine CDNC profile from 28 July 2010 was fairly constant with height. This agrees with the marine clouds of Miles et al [] and Noble and Hudson []. CDNC on 2 September 2014 (continental case) increased at cloud base and top.…”

Section: Resultssupporting

confidence: 90%

“…LWC followed a subadiabatic profile with a subadiabaticity of about 0.18 on 28 July 2010 and 0.07 on 2 September 2014. Increasing LWC from cloud base throughout the cloud was also found by Miles et al [], Hudson and Yum [], and Noble and Hudson []. Uncertainties in the marine (and continental) case were about 43% (45%), 7% (8%), and 21% (24%) for CDNC, r eff , and LWC, respectively.…”

Section: Resultssupporting

confidence: 70%

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Six years of surface remote sensing of stratiform warm clouds in marine and continental air over Mace Head, Ireland

et al. 2016

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A total of 118 stratiform water clouds were observed by ground‐based remote sensing instruments at the Mace Head Atmospheric Research Station on the west coast of Ireland from 2009 to 2015. Microphysical and optical characteristics of these clouds were studied as well as the impact of aerosols on these properties. Microphysical and optical cloud properties were derived using the algorithm SYRSOC (SYnergistic Remote Sensing Of Clouds). Ground‐based in situ measurements of aerosol concentrations and the transport path of air masses at cloud level were investigated as well. The cloud properties were studied in dependence of the prevailing air mass at cloud level and season. We found higher cloud droplet number concentrations (CDNC) and smaller effective radii (reff) with greater pollution. Median CDNC ranged from 60 cm−3 in marine air masses to 160 cm−3 in continental air. Median reff ranged from 8 μm in polluted conditions to 10 μm in marine air. Effective droplet size distributions were broader in marine than in continental cases. Cloud optical thickness (COT) and albedo were lower in cleaner air masses and higher in more polluted conditions, with medians ranging from 2.1 to 4.9 and 0.22 to 0.39, respectively. However, calculation of COT and albedo was strongly affected by liquid water path (LWP) and departure from adiabatic conditions. A comparison of SYRSOC results with MODIS (Moderate‐Resolution Imaging Spectroradiometer) observations showed large differences for LWP and COT but good agreement for reff with a linear fit with slope near 1 and offset of −1 μm.

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Section: Resultssupporting

confidence: 90%

Section: Resultssupporting

confidence: 70%

Six years of surface remote sensing of stratiform warm clouds in marine and continental air over Mace Head, Ireland

et al. 2016

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“…This is probably not a problem for retrieved r e based on the VIIRS Imager (30), because it is lower by a similar amount with respect to MODIS r e . The retrieval uncertainty of r e itself is roughly ±10% (36). This translates to uncertainty of a factor of ±33% in N a .…”

Section: Discussionmentioning

confidence: 98%

“…To avoid significant distortion of r e by coalescence, we avoided heavily precipitating clouds at their tops (r e 0> 18 μm). MODIS r e is larger than aircraft in situ measurements by 10-15% (34)(35)(36). This is probably not a problem for retrieved r e based on the VIIRS Imager (30), because it is lower by a similar amount with respect to MODIS r e .…”

Section: Discussionmentioning

confidence: 99%

“…The observed 26% underestimate in CCN could have been caused by a 10% systematic overestimate in the retrieved r e . This is quite probable, because MODIS-retrieved r e was found to be larger by 10-15% than aircraft in situ measurements (34)(35)(36). An underestimate of satellite-versus surface-measured CCN can be also caused by a systematic decrease of CCN number concentration (N CCN ) between the surface and cloud base heights.…”

Section: [4]mentioning

confidence: 98%

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Satellite retrieval of cloud condensation nuclei concentrations by using clouds as CCN chambers

Rosenfeld

Zheng

Hashimshoni

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

122

130

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Quantifying the aerosol/cloud-mediated radiative effect at a global scale requires simultaneous satellite retrievals of cloud condensation nuclei (CCN) concentrations and cloud base updraft velocities (W b ). Hitherto, the inability to do so has been a major cause of high uncertainty regarding anthropogenic aerosol/cloud-mediated radiative forcing. This can be addressed by the emerging capability of estimating CCN and W b of boundary layer convective clouds from an operational polar orbiting weather satellite. Our methodology uses such clouds as an effective analog for CCN chambers. The cloud base supersaturation (S) is determined by W b and the satellite-retrieved cloud base drop concentrations (N db ), which is the same as CCN(S). Validation against ground-based CCN instruments at Oklahoma, at Manaus, and onboard a ship in the northeast Pacific showed a retrieval accuracy of ±25% to ±30% for individual satellite overpasses. The methodology is presently limited to boundary layer not raining convective clouds of at least 1 km depth that are not obscured by upper layer clouds, including semitransparent cirrus. The limitation for small solar backscattering angles of <25°restricts the satellite coverage to ∼25% of the world area in a single day. (1) states that the uncertainty in aerosol/cloud interactions dominates the uncertainty about the degree of influence that human activities have on climate. Because clouds form in ascending air currents, whereas cloud droplets nucleate on aerosols that serve as cloud condensation nuclei (CCN), we need accurate measurements of both updrafts and CCN supersaturation (S) spectra before we can disentangle aerosol effects on cloud radiative forcing (CRF) from dynamical effects. Need for Global Measurements of Cloud Base Updrafts and CCN(S)Tackling the global change problems as identified by the IPCC requires that these quantities be measured on a global scale. However, satellites have not been able to measure updraft speed of the air that forms the clouds or the concentrations of aerosols that are capable of forming cloud drops, which are ingested into the clouds as they grow. Lack of such fundamental quantities has greatly hindered our capability of disentangling the effects of meteorology and anthropogenic aerosol emissions on cloud properties (2). This situation is starting to change with our recently developed methodology to retrieve updrafts at cloud base (3, 4) using the Visible/Infrared Imager Radiometer Suite (VIIRS) instrument onboard the Suomi National Polar-orbiting Partnership (NPP) satellite. This satellite is sun-synchronous, with an overpass time near 13:30 solar time.Missing such fundamental quantities as CCN(S) and cloud base updraft W b has been preventing us from disentangling the effects of aerosols from atmospheric dynamics (i.e., meteorology). Their absence also has limited our ability to validate the hypothesized impacts of added aerosols on a large range of phenomena, including (i) maintaining full cloud cover in marine stratocumulus, thus incurring a str...

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The impact of cloud vertical profile on liquid water path retrieval based on the bispectral method: A theoretical study based on large‐eddy simulations of shallow marine boundary layer clouds

et al. 2016

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Passive optical retrievals of cloud liquid water path (LWP), like those implemented for Moderate Resolution Imaging Spectroradiometer (MODIS), rely on cloud vertical profile assumptions to relate optical thickness (τ) and effective radius (re) retrievals to LWP. These techniques typically assume that shallow clouds are vertically homogeneous; however, an adiabatic cloud model is plausibly more realistic for shallow marine boundary layer cloud regimes. In this study a satellite retrieval simulator is used to perform MODIS‐like satellite retrievals, which in turn are compared directly to the large‐eddy simulation (LES) output. This satellite simulator creates a framework for rigorous quantification of the impact that vertical profile features have on LWP retrievals, and it accomplishes this while also avoiding sources of bias present in previous observational studies. The cloud vertical profiles from the LES are often more complex than either of the two standard assumptions, and the favored assumption was found to be sensitive to cloud regime (cumuliform/stratiform). Confirming previous studies, drizzle and cloud top entrainment of dry air are identified as physical features that bias LWP retrievals away from adiabatic and toward homogeneous assumptions. The mean bias induced by drizzle‐influenced profiles was shown to be on the order of 5–10 g/m2. In contrast, the influence of cloud top entrainment was found to be smaller by about a factor of 2. A theoretical framework is developed to explain variability in LWP retrievals by introducing modifications to the adiabatic re profile. In addition to analyzing bispectral retrievals, we also compare results with the vertical profile sensitivity of passive polarimetric retrieval techniques.

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MODIS comparisons with northeastern Pacific in situ stratocumulus microphysics

Cited by 27 publications

References 34 publications

Six years of surface remote sensing of stratiform warm clouds in marine and continental air over Mace Head, Ireland

Six years of surface remote sensing of stratiform warm clouds in marine and continental air over Mace Head, Ireland

Satellite retrieval of cloud condensation nuclei concentrations by using clouds as CCN chambers

The impact of cloud vertical profile on liquid water path retrieval based on the bispectral method: A theoretical study based on large‐eddy simulations of shallow marine boundary layer clouds

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